The amount of time people spend sleeping may affect their weight, study results suggest.

The study looked at people living in rural areas. Previous studies conducted in urban and suburban areas have had similar results, which suggests that sleep loss may play a role in the increasing rates of obesity in the US.

Researchers have proposed that shorter sleep duration may affect levels of two weight-control hormones: reduced levels of leptin, a hormone associated with satiety, and increased levels of ghrelin, associated with hunger.

Dr. Neal D. Kohatsu, an epidemiologist at the California Department of Health Services in Sacramento, and his associates were interested in studying rural populations because obesity rates are higher and lifestyle patterns of nutrition, physical activity, work hours, and sleep differ from those in more populous areas.

Rural populations also have a higher prevalence of suicide and a greater propensity toward other risky health behaviors.

According to the researchers’ report in the Archives of internal Medicine, theirs is the first study evaluating the relationship between sleep duration and body mass index (BMI) in rural settings. BMI reflects weight in relation to height, with 20-25 classified as normal, 25-30 as overweight, and over 30 as obese.

The team analyzed data collected in an agricultural county in southeastern Iowa, from a survey of a random sample of 990 employed adults. The subjects were asked about sleep duration, physical activity associated with employment, symptoms of depression, alcohol consumption, snoring, and other demographic information. Height and weight were measured during the same visit.

There was a straight-line relationship between a higher BMI and lesser amount of sleep. The average BMI ranged from 30.24 among individuals sleeping less than 6 hours per night, to 28.25 for those who slept more than 9 hours at a time.

Kohatsu’s group speculates that “modest but sustained changes in sleep duration could have a clinically significant effect on weight.” They acknowledge, however, that the study doesn’t prove that reduced sleep causes obesity.

SOURCE: Archives of internal Medicine, September 18, 2006.